Bone Tumors and Tumor-like Conditions of Bone
Matthew V. Cronin, MD, Tudor H. Hughes, MBBS , MD , FRCR
Nov 08, 2012Authors & Disclosures
Appl Radiol. 2012;41(10):6-15. © 2012 Anderson Publishing, Ltd.
Abstract and Introduction
Abstract
With bone tumor findings in musculoskeletal radiology, the radiologist’s main goal is to assess whether the lesion is benign or aggressive and to determine if further workup is required. The authors demonstrate how contrast-enhanced MRI helps determine tumoral extent and risks, how CT may reveal occult, pathologic fractures, and how scintigraphy may be used to distinguish between monostotic and polyostotic lesions.
Introduction
Bone tumors are a relatively infrequent finding in musculoskeletal radiology. When evaluating osseous lesions, the radiologist’s main goal is to assess whether the lesion is benign or aggressive in appearance and whether further workup is required. The list of potential osseous lesions is extensive; this review of bone tumors does not include metabolic or degenerative lesions. To provide a meaningful differential diagnosis to the referring clinician, several characteristics of every osseous lesion should be routinely assessed.
Classically, 10 radiographic features of a bone lesion should be examined. Five of these include: zone of transition (ZOT), presence or absence of periostitis, location in the bone, pattern of osseous destruction, and age of the patient, along with associated symptoms.[1–3] Additionally, determining if the process is mono-ostotic or polyostotic can be very helpful. Because these characteristics are so important to properly classifying bone tumors, more should be said about each.
The zone of transition is that outer margin of the lesion that represents the change from pathologic to normal bone. A wide ZOT is said to be present when the lesion cannot be clearly circumscribed; this is usually associated with an aggressive lesion. Malignancies such as Ewing ‘s sarcoma and osteosarcoma typically show this pattern of involvement; however, infection and other benign processes, such as eosinophilic granulomas (EG) (Figure 1), can have wide margins. A wide ZOT does not equate to malignancy, but it is very rare for a narrow ZOT (a geographic lesion) to be associated with anything other than a benign lesion.[3,4]
Figure 1.
Eosinophilic granuloma. (A) Frontal radiograph and (B) coronal reformatted CT images from a 2-year-old boy with a high ESR and no fever. The lesion has ill-defined margins and an associated periosteal reaction.
The location of the lesion in the bone, both transversely and longitudinally, can also be useful in narrowing the differential. For example, a select group of lesions is eccentrically located and involves the cortex (osteoid osteoma, parosteal osteosarcoma, and nonossifying fibroma) (Figure 2). Other lesions almost always involve the epiphysis (giant cell tumor after physeal closure (Figure 3), chondroblastoma). Some lesions, such as solitary bone cysts (Figure 4), enchondromas (Figure 5), EG and Ewing ‘s sarcoma, tend to be centrally located.[1,3]
Figure 2.
Nonossifying fibroma with secondary aneurysmal bone cyst formation. Lateral radiograph (A) and (B) axial T2-weighted MRI with fat saturation of the distal tibia in a 14-year-old boy. The radiograph shows a mildly expansile lytic eccentric metaphyseal lesion posteriorly in the distal tibia. The MRI shows the lesion to be mildly loculated with central low signal and a thin rim of high signal, and a single lobule with a fluid-fluid level due to secondary ABC formation.
Figure 3.
Giant cell tumor of bone. (A) Frontal radiograph, (B) surface-rendered 3D CT and (C) repeat frontal radiograph taken 3 months later of the distal forearm in a 27-year-old woman. The expansile lytic subchondral nature of the lesion and in this case its very aggressive increase in size over 3 months is well demonstrated.
Figure 4.
Simple bone cyst. (A) Frontal and (B) axial radiographs of the proximal humerus in a 5-year-old boy. There is a well-defined lucency of the proximal humeral metaphysis with a pathologic fracture. In this case there is no fallen fragment sign as can occur when a fracture fragment migrates through the fluid to lie dependently.
Figure 5.
Enchondroma. (A) Frontal and (B) oblique radiographs of the distal femur. The lesion has the classic appearance for this location with a rings-and-arcs pattern of calcification in a central metaphyseal position.
The number of osseous lesions can also provide clues to etiology. Several lesions that can be polyostotic include multiple hereditary exostoses, enchondromas, fibrous dysplasia and, occasionally, eosinophilic granulomas.[3] Of course, metastatic disease and multiple myeloma (Figure 6) are common causes of multiple lesions, but a few bony metastases can present as solitary lesions—especially in renal or thyroid carcinoma.[3,5]
Figure 6.
Multiple myeloma. Axial CT image through the pelvis of a 68-year-old woman. Note the diffuse permeative pattern of bone destruction. The propensity of lesions should suggest myeloma or metastases in this age group.
Elucidating information from periosteal changes can be relatively more difficult. Periostitis is often subtle and can mislead the radiologist attempting to classify a lesion as benign or aggressive. Classic, aggressive-appearing periostitis is described as having an “onion-skin,” “sunburst” (Figure 7), or “hair-on-end” appearance.[2,3] A Codman triangle pattern is another aggressive configuration. Benign patterns are those that, in theory, have had sufficient time to organize and, thus, show solid thick or wavy unilamellar periosteal changes. Use caution when assessing periosteal reactions, as many benign lesions such as infection, EG (Figure 1), and aneurysmal bone cysts can result in an aggressive-appearing periostitis. Regardless, recognizing periosteal reaction of any type remains important, as this effectively excludes several lesions from the differential. If periostitis is present, fibrous dysplasia, solitary bone cyst, nonossifying fibromas, and enchondromas can be removed from consideration unless complicated by fracture.[3,4]
Figure 7.
Osteogenic sarcoma. (A) Frontal and (B) lateral radiographs of the tibia/fibula in a 15-year-old boy demonstrate a proximal tibia diaphyseal aggressive bone-forming tumor with a large soft-tissue mass. The periosteal reaction has an aggressive “Sun ray spiculation” pattern.
Two additional pieces of information that can be extremely helpful are the age of the patient and the presence or absence of pain. Some lesions, such as Ewing ‘s sarcoma and primary osteosarcoma, are seen overwhelmingly only in the pediatric, adolescent, and young adult populations. Likewise, EG, chondroblastoma, solitary and aneurysmal bone cysts are rarely seen in adults >30 yrs. Moreover, while infection, metastatic lesions, and aneurysmal bone cysts typically present with pain, discomfort is rare (in the absence of trauma) with fibrous dysplasia, enchondromas, and solitary bone cysts. Several other characteristics, such as the presence of sclerotic margins, soft tissue involvement, a pattern of bony destruction, endosteal scalloping, and the pattern of matrix calcification, can also aid in diagnosis.
Although plain radiographs, computed tomography (CT), magnetic resonance imaging (MRI), and radionuclide studies may each provide additional information, suspected soft-tissue extension of an osseous lesion should be evaluated further with contrast-enhanced MRI to determine not only tumoral extent but also the risk of complications like neurovascular compromise. Also, MRI may help narrow the list of differential considerations by demonstrating cystic or necrotic components, encapsulation, contrast enhancement and the presence of fluid levels (Figures 2, 8, 9) or peritumoral edema on MRI. Dedicated CT may show occult, pathologic fracture in an otherwise benign-appearing but painful lesion.
Figure 8.
Aneurysmal bone cyst. (A) Lateral radiograph, (B) axial bone and (C) soft-tissue window CT and (D) axial T2 with fat saturation MRI of the distal left tibia in a 25-year-old man with aneurysmal bone cyst. Note the expansile nature of the lytic lesion with a thin rim of intact bone and the multiple fluid-fluid levels from the stagnant pooling of blood on the soft tissue CT and MRI.
Figure 9.
Telangiectatic osteosarcoma. (A) Frontal radiograph, (B) MDP bone scan and (C) axial T2-weighted MRI with fat saturation show a lesion in the lateral aspect of the right distal femur meta-epiphysis of a 19-year-old man. This version of osteosarcoma is relatively lytic compared to the conventional osteosarcoma, but it shows marked uptake on MDP. The axial MRI shows multiple fluid levels, strongly suggestive of the diagnosis.
Scintigraphy with Tc99m–MDP bone scan can determine whether a lesion is mono-ostotic versus polyostotic in nature. The following is a brief description of each of the 15 most common benign and malignant osseous lesions the radiologist is most likely to encounter.
Section 1 of 4
Next: Benign Bone Lesions
Appl Radiol. 2012;41(10):6-15. © 2012 Anderson Publishing, Ltd.
Bone Tumors and Tumor-like Conditions of Bone
Matthew V. Cronin, MD, Tudor H. Hughes, MBBS , MD , FRCR
Nov 08, 2012Authors & Disclosures
Appl Radiol. 2012;41(10):6-15. © 2012 Anderson Publishing, Ltd.
Benign Bone Lesions
Solitary Bone Cysts
As mentioned previously, solitary bone cysts tend to be centrally located, painless lesions occurring almost exclusively in patients <30 yrs These tumors appear lytic, have a narrow ZOT and are most often located in the proximal humerus and femur (Figure 4). There is no periostitis unless an associated fracture is present. A fracture through an SBC may show the classic “fallen fragment” sign, which is fractured bone that has fallen to the most dependent portion of the cyst.[3,4] As expected for a cystic structure, the MRI appearance of these lesions shows hypointense T1 and hyperintense T2 characteristics.
Aneurysmal Bone Cysts (ABC)
These metaphyseal lesions are seen almost exclusively in patients <30 years of age. In contrast to a unicameral or solitary bone cyst, an ABC is typically painful, can have periostitis (often aggressive) and is eccentrically located. The ZOT is usually narrow and an expansile bubbly appearance is common (Figures 2, 8). An ABC should be considered in the differential (along with osteoblastoma, tuberculosis, and osteoid osteoma) for lesions in the posterior elements of the spine. ABC often complicates other lesions, most notably chondroblastoma, osteoblastoma and giant cell tumor of bone. The MR and CT appearances may show fluid-fluid levels, which is a nonspecific finding and can be seen in other lesions, including chondroblastoma, giant cell tumor of bone, or telangiectatic osteosarcoma.[3,6–9]
Fibrous Dysplasia
This painless, typically metadiaphyseal lesion can be monoostotic or polyostotic. When polyostotic, fibrous dysplasia is overwhelmingly (90%) located on one side of the body.[3] The ZOT is narrow and the lesion itself can be quite heterogeneous with a lytic, sclerotic, or mixed appearance (Figure 10). When located in the pelvis, fibrous dysplasia can often appear lytic and bubbly while rib lesions may have a ground-glass appearance and be expansile. Involved tubular bones are expanded and demonstrate cortical thinning. In the hip, this can lead to varus angulation and a “Shepherd’s crook” deformity of the femoral neck.[3,6,8,10] The skull base and calvarium are also common sites of involvement. There is no periostitis and the age range of affected patients is broad. The MRI appearance is nonspecific, typically showing T1 prolongation and variable T2 intensity.
Figure 10.
Fibrous dysplasia. (A) Frontal and (B) magnified view of (A), views of the left tibia/fibula in an 11-year-old boy. Note the mildly expansile nature of the dysplastic bone with cortical thinning and on the expanded view the ground-glass nature of the bone matrix.
Nonossifying Fibroma
This common lesion is cortically based and eccentrically located. Found in individuals between 2 and 30 years, the painless entity shows a narrow ZOT with sclerotic borders and an appearance that can range from lytic initially to entirely sclerotic in the latter stages of development, as they typically “heal” and appear ossified (Figure 2). There is no associated periostitis. The MR appearance is nonspecific, with low signal on T1-weighted images and variable T2 signal.[3,6–8]
Giant Cell Tumor
This geographic, lytic lesion is classically described as having 4 qualifying characteristics when found in the long bones. It is eccentrically located, has a sharp nonsclerotic ZOT, abuts subchondral bone, and almost always occurs in individuals with recently closed physes (Figure 3). The most common locations are distal femur, proximal tibia and distal radius. However, atypical locations such as the pelvis and calcaneus are also seen.[3,6,7,9,11] In these cases, giant cell tumors need not conform to the above criteria. These lesions are usually mono-ostotic; however, polyostotic tumors or satellite lesions are rarely seen and can be difficult to differentiate from metastatic GCT. Periostitis is not present. There is low signal on T1 and variable T2 MRI signal, which may include hyperintense regions or fluid levels secondary to aneurysmal bone cysts.
Eosinophilic Granuloma
Eosinophilic granuloma (EG) could also be called the great mimicker of osseous lesions. While EG typically is found only in patients<30 years, there are a few other discriminating characteristics. For example, EG may appear lytic, sclerotic, mixed or “moth-eaten” (Figure 1). The ZOT can be narrow or wide. Associated periostitis may cause this lesion to appear aggressive. Infrequently, a bony sequestrum may be present; however, this can also be seen in osteomyelitis, fibrosarcoma and primary lymphoma of bone.[3,6,8,12] Most EG lesions are monoostotic, but younger patients are at higher risk for developing polyostotic disease.
Enchondroma
Enchondromas are centrally located, geographic, and predominantly lytic-appearing lesions, which almost invariably contain a chondroid matrix when found in the long bones (Figure 5). These monoostotic, painless lesions may show endosteal scalloping; however, there is no associated periostitis. Enchondromas may be difficult to discriminate from low-grade chondrosarcomas, but the latter is more likely in a history of pain, cortical destruction or soft tissue extension.[13] Large or proximal lesions have an increased rate of malignant transformation. In contrast, enchondromas found in the hands and feet may be polyostotic, but they rarely undergo malignant transformation except in Ollier’s disease or associated with soft-tissue hemangiomas, as in Maffucci’s syndrome.[3,6] Chondroid matrix is conspicuously absent in these peripheral lesions.
Osteochondroma
This lesion arises from the metaphyseal region of the long bones as a bony excrescence contiguous with the medullary compartment that characteristically points away from the adjacent joint. Osteochondromas are typically solitary, appendicular lesions, which cease growing after the skeleton matures (Figure 11). Growth after this point, cortical erosion, or thickening of the associated cartilaginous cap is rare, but suggestive of malignant transformation into chondrosarcoma.[3,6,14,15] Multiple hereditary exostoses are a rare, autosomal dominant, polyostotic form of the disease that has an increased risk of malignant transformation.
Figure 11.
Osteochondroma. AP radiograph in a 25-year-old man shows the classic appearance of a metaphyseal lesion directed away from the adjacent joint with continuation of the medullary space into the lesion. These often cause mechanical problems and may develop an
Appl Radiol. 2012;41(10):6-15. © 2012 Anderson Publishing, Ltd
Bone Tumors and Tumor-like Conditions of Bone
Matthew V. Cronin, MD, Tudor H. Hughes, MBBS , MD , FRCR
Nov 08, 2012Authors & Disclosures
Appl Radiol. 2012;41(10):6-15. © 2012 Anderson Publishing, Ltd.
Malignant Bone Lesions
Osteosarcoma
In patients <30 years, osteosarcoma and Ewing ‘s sarcoma are the most common primary malignant tumors of bone. Osteosarcoma can be subdivided into medullary, parosteal, periosteal and telangiectatic, all of which carry different prognoses and treatment options.
Medullary osteosarcoma (Figure 7) is the most common, occurring in adolescents and young adults typically between the ages of 15 and 25 yrs. These are rapidly growing, heterogeneous, metaphyseal lesions that show cortical destruction, aggressive periostitis, and a wide ZOT. Osseous matrix formation is the norm and a soft tissue component is often present. Evaluation with MRI shows variable T1 and T2 signal characteristics secondary to varying degrees of ossification. High T2 signal is often seen around the periphery of the lesion, presumably related to adjacent edema. Metastatic skip lesions are commonly seen and should be worked up with radionuclide evaluation.
Parosteal osteosarcoma (Figure 12) originates from the parosteal soft tissues and is less aggressive than the medullary form. This lesion typically occurs in older patients. Growth is circumferential around the involved bone and typically does not initially result in cortical destruction. As such the prognosis for this lesion is more favorable. However, if intramedullary extension does occur, the prognosis is more guarded.
Parosteal osteosarcoma. (A) Frontal and (B) lateral radiographs of the distal femur in a 16-year-old male demonstrate florid new bone formation projecting medially, laterally, and posteriorly.
radiographic appearance of Ewing ‘s is nonspecific and can overlap that seen with infection or eosinophilic granuloma. MRI characteristics show low signal on T1, high signal on T2, and typically an adjacent soft-tissue mass that may be heterogeneous in appearance secondary to focal necrosis.[3,4,7]
Figure 13.
Ewing’s sarcoma. (A) Frontal and (B) lateral radiographs, (C) sagittal T1 and (D) coronal T2 with fat saturation MRI of the left humerus in a 15-year-old girl with arm pain and a mass. There is a permeative mixed lytic and sclerotic lesion involving the distal humeral shaft with accompanying periosteal reaction. The MRI shows a nonspecific low T1, high T2-signal pattern and soft-tissue involvement.
Chondrosarcoma
Chondrosarcoma is typically a low-grade malignant osseous tumor found in adults. The radiographic appearance can be misleading, as often few aggressive features are present. This is a lytic, metaphyseal-based lesion, which may have a “snowflake” chondroid matrix. However, completely lytic lesions are not unusual (Figure 14). Cortical erosion, soft-tissue extension, and pain may or may not be present. Low-grade chondrosarcoma can be difficult, if not impossible, to differentiate from an enchondroma, which is the primary alternative consideration in the differential diagnosis. On MRI, low grade, differentiated chondrosarcomas will appear bright on T2 imaging, with more homogeneous signal than that of higher-grade lesions.[3,4]
Figure 14.
Chondrosarcoma. (A) Frontal radiograph, (B) axial CT, (C) sagittal-T2 and (D) sagittal-T1, fat-saturated, post-gadolinium MRI of a 34-year-old man with a sacral chondrosarcoma. There is a large necrotic tumor with enhancing margins surrounding the central rings-and-arcs pattern of calcified matrix arising from the sacrum.
Osseous metastatic lesions have multiple appearances and therefore are often included in the differential for atypically appearing sclerotic or lytic lesions. Several metastatic lesions, such as renal cell, thyroid, melanoma, and choriocarcinoma, are classically lytic in appearance. However, other than renal cell cancer, this need not always be the case. Metastatic prostate cancer (Figure 16) will typically show sclerotic lesions, but breast, lung (Figure 17) and gastrointestinal malignancies can also mimic this appearance. As is the case with other lesions, MRI is useful for evaluation of soft tissue extent and staging; however, biopsy is needed for diagnosis.[3–5]
Multiple myeloma is a diffuse, permeative malignancy found in adults over the age of 35 to 40 yrs. While this lesion is typically lytic, a rare form of sclerotic myeloma is seen in association with POEMS syndrome (Polyneuropathy, Organomegally, Endocrinopathy, Monoclonal gammopathy and Skin changes). In the early stages, myeloma may be preceded by a predominantly lytic plasmacytoma that is usually found in the axial skeleton. Multiple myeloma ultimately ensues, typically with a diffuse axial and appendicular distribution. Multiple “punched out” lesions in the calvarium and axial skeleton are a classic appearance of this disease (Figure 6). Patients inevitably suffer from renal failure secondary to Bence-Jones protein deposition or associated amyloidosis. Of note, radionuclide studies with Tc99m-MDP are ineffective in demonstrating myelomatous lesions.[3,4]
Conclusion
This article has reviewed the commonest benign and malignant bone tumors the radiologist is likely to encounter. To construct a meaningful differential diagnosis, an attempt should be made to characterize the lesion as having either an aggressive or a benign appearance by assessing such qualities as the zone of transition, periostitis, pattern of lysis, and location. A careful and methodical analysis will help the radiologist determine if the lesion is likely benign or if additional workup or biopsy should be considered.